It allows creating a RAM based block device which acts as swap disk.Pages swapped to this device are compressed and stored in memory itself.This is a big win over swapping to slow hard-disk which are typically usedas swap disk. For flash, these suffer from wear-leveling issues when usedas swap disk - so again its helpful. For swapless systems, it allows moreapps to run.

* Changelog: take4 vs take3xvmalloc changes: - Fixed regression in take3 that caused ramzswap write failures. This happened due to error in find_block() where we did not do explicit cast to 'unsigned long' when checking for bits set in bitmap. Now changed it to use kernel build-in test_bit(). - Fix divide by zero error in proc read function.ramzswap changes: - Forward write requests to backing swap device if allocation for compressed page fails. - Code cleanups.

(Please also see testing notes below).

* Changelog: take3 vs take2xvmalloc changes: - Use kernel defined macros and constants in xvmalloc and remove equivalent defines for ALIGN, roundup etc. - Use kernel bitops (set_bit, clear_bit) - Moved it to drivers/block since its not clear if it has any other user.ramzswap changes: - All instances of compcache renamed to ramzswap. Also renamed module to ramzswap - Renamed "backing_dev" parameter to "backing_swap" - Documentation changes to reflect above changes. - Remove "table index" from object header (4 bytes). This will be needed when memory defragmentation is implemented. So, avoid this (small) overhead for now.